Abstract: One of the most significant applications of single-photon sources is secure quantum communication. In this research, the security of the most famous protocol of quantum key distribution (BB84) has been studied by considering the characteristics of a single-photon source. This paper derives the impact of propagation on photon statistics. The result reveals that the propagation leads to a change in its value, especially in long distances. Besides, the parameter deviation from an ideal source causes a decrease in the confident length. We achieved a difference of up to 1800 km for the safe distance by studying the relation for minimum transmission coefficient in available single-photon sources. Keywords: Quantum communication, Quantum key distribution, Security, Single-photon source.
Abstract: One of the most significant applications of single-photon sources is secure quantum communication. In this research, the security of the most famous protocol of quantum key distribution (BB84) has been studied by considering the characteristics of a single-photon source. This paper derives the impact of propagation on photon statistics. The result reveals that the propagation leads to a change in its value, especially in long distances. Besides, the parameter deviation from an ideal source causes a decrease in the confident length. We achieved a difference of up to 1800 km for the safe distance by studying the relation for minimum transmission coefficient in available single-photon sources. Keywords: Quantum communication, Quantum key distribution, Security, Single-photon source.
We investigate the security of quantum key distribution with entangled photons, focusing on the two-photon variation of the Bennett-Brassard 1984 (BB84) protocol proposed in 1992 by Bennett, Brasard, and Mermin (BBM92). We present a proof of security which applies to realistic sources, and to untrustable sources which can be placed outside the labs of the two receivers. The proof is restricted to individual eavesdropping attacks, and assumes that the detection apparatus is trustable. We find that the average collision probability for the BBM92 protocol is the same as that of the BB84 protocol with an ideal single-photon source. This indicates that there is no analog in BBM92 to photon splitting attacks, and that the source can be placed between the two receivers without changing the form of the collision probability. We then compare the communication rate of both protocols as a function of distance, and show that BBM92 has potential for much longer communication distances, up to 170 km, in the presence of realistic experimental imperfections. Finally, we propose a scheme based on entanglement swapping that can lead to even longer distance communication. The limiting factor in this scheme is the channel loss, which imposes very slow communication rates at longer distances.
Single-photon sources are crucial components for the implementation of quantum communication protocols. However, photons emitted by some of the most popular types of realistic sources are spectrally broadband. Due to this drawback, the signal emitted from such sources is typically affected by the effect of temporal broadening during its propagation through telecommunication fibers which exhibit chromatic dispersion. Such problem can be observed e.g. when using sources based on the process of spontaneous parametric down-conversion (SPDC). In the case of long-distance quantum communication temporal broadening can significantly limit the efficiency of temporal filtering. It is a popular method, which is based on the reduction of the duration time of the detection window, used for decreasing the number of registered errors. In this work we analyzed the impact of the type of spectral correlation within a pair of photons produced by the SPDC source on the temporal width of those photons during their propagation in dispersive media. We found out that in some situations the width can be decreased by changing the typical negative spectral correlation into positive one or by reducing its strength. This idea can be used to increase the efficiency of the temporal filtering method. Therefore it can be applied in various implementations of quantum communication protocols. As an example of the application we subsequently analyzed the security of a quantum key distribution (QKD) scheme based on single photons. It was realized in the configuration with the source of photons located in the middle between the legitimate participants of a QKD protocol (called typically Alice and Bob). We demonstrated that when the information about the emission time of the photons produced by the SPDC source is not distributed to Alice and Bob, the maximal security distance can be considerably extended by using positively correlated photons, while in the opposite case strongly (no matter positively or negatively) correlated photons are optimal. We also found out that the results of our calculation may be very sensitive to the spectral widths of the photons produced by the SPDC source. In addition, we concluded that in realistic situation Alice and Bob would have to optimize their source over both the spectral widths of the generated photons and the type of spectral correlation in order to maximally extend the security distance. The results of our work are, in particular, important for the QKD systems utilizing commercial telecom fibers populated by strong classical signals. In those systems temporal filtering method can be used to reduce not only the dark counts registered by the detection system, but also the channel noise originating from the process of Raman scattering, which is the main factor limiting their performance.
In real fiber-optic quantum cryptography systems, the avalanche photodiodes are not perfect, the source of quantum states is not a single-photon one, and the communication channel is lossy. For these reasons, key distribution is impossible under certain conditions for the system parameters. A simple analysis is performed to find relations between the parameters of real cryptography systems and the length of the quantum channel that guarantee secure quantum key distribution when the eavesdropper’s capabilities are limited only by fundamental laws of quantum mechanics while the devices employed by the legitimate users are based on current technologies. Critical values are determined for the rate of secure real-time key generation that can be reached under the current technology level. Calculations show that the upper bound on channel length can be as high as 300 km for imperfect photodetectors (avalanche photodiodes) with present-day quantum efficiency (η ≈ 20%) and dark count probability (p dark ∼ 10−7).
In recent years, quantum communication has emerged as a game-changing technology with the potential to completely revamp the security architecture of the Internet. In this analysis, we look at the potential of quantum communication techniques to improve the safety of sent data and the effectiveness of networked data transmission. Examining well-known quantum communication protocols like BB84, E91, CV-QKD, and MDIQKD in light of their classical analogues is at the heart of this study. The research provides insight into the benefits and hurdles of using quantum communication in secure networking settings by studying a variety of performance measures, such as security levels, key rates, mistake rates, and communication lengths. We used an extensive analytical framework to compare the efficiency of the suggested quantum communication techniques to that of the original protocols. We conducted extensive experiments and analyzed the data to demonstrate the concrete advantages of using quantum communication for increasing security, increasing key rates, decreasing mistake rates, and increasing communication distances. Comparing the BB84 protocol's security grade of 0.98 to that of the conventional method's 0.92 reveals a 6.52 percent increase in safety. Key rates of 9.8 Mbps were achieved using the CV-QKD protocol, which was shown to be an improvement of 30.7% over the standard method's 7.5 Mbps. These results emphasize the unique security characteristics of quantum communication, which are since eavesdropping is very difficult due to the nature of quantum mechanics. In conclusion, this study promotes the use of quantum communication protocols as a reliable and efficient approach to meeting the rising needs for network security. Quantum communication, which makes use of quantum mechanics' benefits, offers a promising future for establishing a safe networking paradigm in the digital age by guaranteeing secure, high-speed, and long-distance data transfer.
The security of quantum key distribution (QKD) is based on the basic principles of quantum mechanics, and therefore has unconditional security in theory. In existing quantum key distribution systems, weakly coherent sources (WCSs) are often used as light sources due to a high probability of vacuum pulses in these sources, resulting in limited transmission distances. Besides, there inevitably exist equipment defects in actual QKD systems, such as certain defects in phase modulators and intensity modulators, which lead to distinguishability of quantum states in higher dimensions and result in side-channel vulnerabilities. An eavesdropper can carry out corresponding attacks, thereby threatening the actual security of QKD systems. To overcome the above limitations, we propose an improved protocol on quantum key distribution based on monitoring heralded single-photon sources. Due to the simultaneity of parametric down-conversion photon pairs, we can accurately predict the arrival of one photon by measuring the arrival time of another photon. Through this way, we can greatly reduce the probability of vacuum states in the signal light, and increase the longest transmission distance of the QKD system. Moreover, a light source monitoring module is inserted into the sender’s side. By randomly selecting a certain period of time through the source monitoring module to measure the Hong-Ou-Mandel interference between the signal light and the idle light , we can estimate the side-channel information leakage of the source and then obtain the key generation rate. Compared with the QKD protocol based on monitoring weak coherent sources, our present protocol can give a better performance in either the transmission distance or the key generation rate, especially when the interference error is large. In addition, in principle, our present protocol can also be extended to other quantum key distribution protocols, such as the measurement-device-independent protocols, to further improve the security and practicability of QKD systems. Therefore, our present work can provide valuable references for realizing the large-scale application of quantum communication networks in the near future.
Introduction: The analysis of the main directions of research in the field of creating sources of single photons for communication systems with quantum key distribution is carried out. Scientometric analysis based on Scopus database is used to identify the most promising areas and predict the trends in the field of single photon sources. Methods of single photon sources development and their applications in commercial communication systems with quantum key distribution is shown. At the time single photons sources based on quantum dots are the most developed and presented on the market. However, color centers in nanocrystals and carbon nanotubes are intensively studied. The prospects of creating compact and easy-to-use sources of single photons on telecommunication wavelengths is analyzed. There are many ways of realization of single photon sources design. Significant funding in China and Germany leads to notable growth of the technology. It was detected the main journals, author groups and organizations working in direction of single photon sources. Methods and Results: The research field of communication systems using sources of single photons is growing. It is available single photon sources on quantum dots and crystals. Applying of carbon nanotubes is promising for this problem according to some famous authors. It is revealed significant overlap of the research areas: single photon sources, quantum random number generators and quantum key distribution. At the time fundamental studies are implemented in technical devices with high potential for commercial applications.